1.3 KiB
lec5
Lab
This lecture will have a lab activity in cst366/lab/1994-census-summary.sql with instructions found in single-table-queries-2-lab.pdf.
Distinct Values
- Mininum - min(field)
Finds the smallest value in the given filed
- Maximum - max(field)
Find the largest value in the given field
Say we have a column where we know there are duplicate values but we want to konw what the distinct values in the column may be.
SQLite3 has a function for that: select distinct field, ... from table;
- select substr(field, startIndex, length) ...
Note: the start index starts counting at 1 so keep in mind we are offset +1 compared to other language like C.
Joins
Now we want to join to tables together to associate their respective data.
To accomplish this we can perform a simple join to combine tables.
Important to note that a simple join does not necessarily take care of duplicate fields.
If we have duplicate fields we must denote them as target.field.
Here target is the table with the desired table and field is the desired field.
Type Casting
If we have say "56" we can use a cast to turn it into an integer.
cast(targetString as integer)
This will return with an error if a non number character is given as input to the cast function, here in this example we denote it with targetString.